Translator for HPLC HINTS and TIPS for Chromatographers

Saturday, August 29, 2015

Terminology. Which is it? UPLC, UHPLC or HPLC? The correct name is still HPLC.

Proper terminology is very important in science. I hear and see people misuse the terms "UPLC" and "UHPLC" often so think we need a short post to clarify the correct use of these terms. Here are some basic definitions.

Some quick background information. "LPLC" or  Low Pressure Liquid Chromatography. LPLC often includes chromatography analysis using glass or plastic columns with very large particle support beads run at pressures ranging from atmospheric (gravity driven) to several hundred psi (~ 30 - 40 bars max). Very large particles are required in this application to aid flow through the support, which in some cases is gravity driven and in others, a small pump is used.

"HPLC" or High Performance Liquid Chromatography: *Used to be called High Pressure Liquid Chromatography to differentiate it from "LPLC". Now we refer to it as "high performance" chromatography, though both terms are technically correct. Compared to the very large media used in LPLC (mm), HPLC uses micron sized support particles packed under very high pressures in stainless steel (note: sometimes strong rigid plastic columns are used for biocompatible applications) columns to enhance the resolution obtained by many orders of magnitude. As such, the more popular definition changed from "High Pressure" to "High Performance" Liquid Chromatography to emphasize this improvement. Today, we still refer to all modes of high pressure liquid chromatography separation techniques as "HPLC". The most commonly used HPLC pumps are rated between 400 and 600 bars maximum pressure (with some capable of 1,200 bars or more) though in normal use, we rarely run methods which use pressures over 300 bars.

"UHPLC" or Ultra High Pressure Liquid Chromatography (or Ultra High Performance Liquid Chromatography) has become both a new marketing term and perhaps a subcategory of HPLC (other subcategory examples include: nano-HPLC, narrow-bore HPLC, and mini-bore HPLC). UHPLC is presently defined as the use of sub-2 μm particles with a low dispersion HPLC system where the pump is capable of > 600 bars pressure. UHPLC is still HPLC. Many methods which use sub-2 μm particle columns can and are run on a low dispersion HPLC system at pressures which do not exceed 400 or 600 bars [For more information, please read: "Pressure Drop Across an HPLC / UHPLC Column"]. The technique used in all cases is still HPLC and should be described as such. We have been using narrow bore columns with small supports for more than 30 years and never have changed the name of the technique used each time we changed the column type used (e.g. 20u, 10u, 5u, 3.5u, 2,5u...). As a matter of fact, in the late 1980's and early 1990's there was a bug push to use 1.0, 2.1 and 3.5 mm ID columns with 3.5u and smaller particles on low dispersion systems to both save solvent, increase performance and reduce run times. This required the use of HPLC systems which were optimized with low dispersion flow paths such as the HP 1090 HPLC system. Perhaps the technology and methods came too early? Columns proved difficult to pack with the smaller particles (poor RSD). The solvent savings and reduced run times just did not interest people at that time and after a few years, the lack of interest resulted in few commercial columns being available with these properties (I recall packing many of them myself in the lab).

"UPLCTM" or Ultra-Performance Liquid Chromatography is a Trademark of the Waters Corporation. Waters Corporation uses it as a marketing term for their own product technology. Defined by Waters as, "the use of sub-2 μm particle columns in combination with low dispersion, high pressure (15,000 psi or 1,034 bar) instrumentation". The confusion seems to come from people using the Water's trademark of "UPLC" to describe the technique of HPLC or an HPLC system with a pump which is capable of exceeding 600 bars pressure or having a low dispersion flow path. They should be using the term HPLC in these cases or even UHPLC, if applicable, not "UPLC" (unless they really are referring to the Waters product technology).

Summary: In general, as long as the back pressure is above ~30 bars and/or you are using packed columns with porous particles less than ~ 50 microns in diameter (newer, monolithic supports and superficially porous particles also qualify), then the technique used is always called HPLC. If you are using sub-2μm particles and operating at pressures at or above 600 bars, then the term "UHPLC" could be used as well (not UPLC® unless you are specifically using a Waters Corp "UPLC" brand system under the same conditions described), but the term HPLC is far more accurate. You are always correct describing the techniques used as HPLC.

3 comments:

  1. Thanks for explaining this. Sounds like vendors made up the name to convince customers that the system they have is no good and they need to buy a more expensive system with a different label on it!

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  2. I wonder how many high pressure systems (>800 bar) are still running 10-20 minute methods at 'regular hplc' resolutions.

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  3. You would think that scientists would know that the 'U' in UHPLC (or UPLC) was just a marketing campaign to convince users that they needed to buy new HPLC systems with higher max pressure ratings? It seems that some were ignorant and swept up in the sales adverts. We should not call it "UHPLC" at all, but HPLC. All high pressure liquid chromatography is HPLC. Running at higher pressures or using smaller particles would have meant that we would have changed the name everytime we reduced particle size or ran at higher pressures (which we did not do because the name HPLC took care of it). UHPLC is not novel or unique at all. It is still high performance liquid chromatography. HPLC by definition has NEVER specified a specific pressure or particle size. Once we went from "LC" to "HPLC", that name change took care of ALL changes needed. All methods which run at any pressure substantially above gravity flow system (as used in "LC" systems) with packed columns are HPLC methods, not UHPLC or UPLC methods.

    'HPLC Expert' is correct. Let's stop making up new names for a technique that already has one. To do otherwise makes us scientists look ignorant.

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